Methods for forming dielectric layers

ABSTRACT

Methods for forming a dielectric layer on a substrate are provided herein. In some embodiments a method for forming a dielectric layer on a substrate may include exposing the substrate to a first source gas comprising a silicon (Si) precursor and an oxidizer for a first period of time to form a first layer comprising silicon and oxygen; and exposing the substrate to a second source gas comprising a metal precursor and the silicon precursor for a second period of time to form a second layer comprising silicon and a metal, where in the first layer and the second layer form the dielectric layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of U.S. provisional patent applicationSer. No. 61/226,375, filed Jul. 17, 2009, which is herein incorporatedby reference in its entirety.

FIELD

Embodiments of the present invention generally relate to substrateprocessing and, more particularly, to methods of forming dielectriclayers on substrates via atomic layer deposition (ALD).

BACKGROUND

In the field of semiconductor, flat-panel display, or other electronicdevice processing, vapor deposition processes have played an importantrole in depositing materials on substrates. As the geometries ofelectronic devices continue to shrink and the density of devicescontinue to increase, overall feature size has decreased and aspectratio has increased. While conventional chemical vapor deposition (CVD)processes have proved successful, shrinking device geometries require analternative deposition technique, such as atomic layer deposition (ALD).

A conventional ALD process involves sequentially exposing a substrate tochemical precursors and reactants. Typically, a chemical precursor isprovided to a process chamber having a substrate, which is adsorbed ontothe surfaces of the substrate. A reactant is then provided to theprocess chamber, which reacts with the chemical precursor, resulting ina deposition of material.

ALD processes generally allow for improved coverage of surfaces withinsubstrate features over a conventional CVD process. However, ALD processtypically have slower deposition rates than comparable CVD processes fordepositing materials having similar compositions.

Therefore, a need exists for an improved method of processing substratesusing ALD.

SUMMARY

Methods for forming a dielectric layer on a substrate are providedherein. In some embodiments a method for forming a dielectric layer on asubstrate may include exposing the substrate to a first source gascomprising a silicon (Si) precursor and an oxidizer for a first periodof time to form a first layer comprising silicon and oxygen; andexposing the substrate to a second source gas comprising a metalprecursor and the silicon precursor for a second period of time to forma second layer comprising silicon and a metal, where in the first layerand the second layer form the dielectric layer.

In some embodiments, methods for forming a dielectric layer may includeexposing the substrate to a first source gas comprising a siliconprecursor and an metal precursor for a first period of time to form afirst layer comprising silicon and a metal; and exposing the substrateto a second source gas comprising a silicon precursor and an oxidizerfor a second period of time to form a second layer comprising siliconand oxygen, wherein the first layer and the second layer form thedielectric layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, briefly summarized above anddiscussed in detail below, can be understood by reference to theillustrative embodiments of the invention depicted in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only exemplary embodiments of this invention and aretherefore not to be considered limiting of its scope, for the inventionmay admit to other equally effective embodiments.

FIG. 1 depicts a method for forming a dielectric layer on a substrate inaccordance with some embodiments of the present invention.

FIG. 2 depicts an apparatus suitable for processing semiconductorsubstrates in accordance with some embodiments of the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

Embodiments of the present invention generally relate to methods offorming dielectric layers on substrates via atomic layer deposition. Theinventive methods may advantageously increase productivity andefficiency of processing semiconductor substrates and further mayprovide a dielectric layer with significant improvement in one or moreof compositional uniformity, thickness uniformity, and increases rate ofdeposition.

FIG. 1 depicts a method for forming a dielectric layer on a substrate inaccordance with some embodiments of the present invention. The abovemethod may be performed in any apparatus suitable for processingsubstrates in accordance with embodiments of the present invention, suchas discussed below with respect to FIG. 2.

The method 100, begins at 102, where a substrate, having a surface uponwhich a dielectric layer is to be formed, is provided. As used herein, a“substrate surface” refers to any substrate surface upon which a layermay be formed. The substrate surface may have one or more featuresformed therein, one or more layers formed thereon, and combinationsthereof. The substrate (or substrate surface) may be pretreated prior tothe deposition of the dielectric layer, for example, by polishing,etching, reduction, oxidation, halogenation, hydroxylation, annealing,baking, or the like.

The substrate may be any substrate capable of having material depositedthereon, such as a silicon substrate, a III-V compound substrate, asilicon germanium (SiGe) substrate, an epi-substrate, asilicon-on-insulator (SOI) substrate, a display substrate such as aliquid crystal display (LCD), a plasma display, an electro luminescence(EL) lamp display, a solar array, solar panel, a light emitting diode(LED) substrate, a semiconductor wafer, or the like.

Next, at 104, a dielectric layer is formed on the substrate. In someembodiments, the dielectric layer may be deposited via a cyclicaldeposition process, for example, such as atomic layer deposition, or thelike. In some embodiments, the dielectric layer is a high-K dielectriclayer, for example, having a dielectric constant equal to or greaterthan about 9. In some embodiments, the dielectric layer is a metalsilicate film, such as, for example, hafnium silicate (HfSiO_(x)),hafnium silicon nitride (Hf_(x)Si_(y)N), aluminum silicon oxynitride(AlSi_(x)O_(y)N_(z)), or the like. The subscripts (x,y,z) imply thatstoichiometry or composition may be intentionally varied via sequencesof the cyclical deposition process to form the compounds.

In some embodiments, the forming of a dielectric layer via a cyclicaldeposition process may generally comprise exposing the substrate to twoor more source gases sequentially. In some embodiments, each source gasmay be separated by a time delay/pause to allow the components of thesource gas to adhere and/or react on the substrate surface. For example,a first source gas may be dosed/pulsed into a reaction zone followed bya first time delay/pause. Next, a second source gas may be dosed/pulsedinto the reaction zone followed by a second time delay. This sequencemay be repeated until a desired layer thickness is formed on thesubstrate surface.

A “reaction zone” is intended to include any volume that is in fluidcommunication with a substrate surface being processed. The reactionzone may include any volume within a processing chamber that is betweena gas source and the substrate surface. For example, the reaction zoneincludes any volume in which a substrate is disposed that is downstreamof a dosing valve.

A “pulse/dose” as used herein is intended to refer to a quantity of asource gas that is intermittently or non-continuously introduced into areaction zone of a process chamber. The quantity of a particularcompound within each pulse may vary over time, depending on the durationof the pulse. A particular source gas may include a single compound or amixture/combination of two or more compounds.

The durations for each pulse/dose are variable and may be adjusted toaccommodate, for example, the volume capacity of the processing chamberas well as the capabilities of a vacuum system coupled thereto.Additionally, the dose time of a source gas may vary according to theflow rate of the source gas, the temperature of the source gas, the typeof control valve, the type of process chamber employed, as well as theability of the components of the source gas to adsorb onto the substratesurface. Dose times may also vary based upon the type of layer beingformed and the geometry of the device being formed. In some embodiments,the duration for each pulse/dose or “dose time” may be about 12 secondor less. However, a dose time can range from microseconds tomilliseconds to seconds, and even to minutes. A dose time should be longenough to provide a volume of compound sufficient to adsorb/chemisorbonto substantially the entire surface of the substrate and form a layerof the source gas component thereon.

In some embodiments, each source gas may be separated by a timedelay/pause to allow the components of the source gas to adhere and/orreact on the substrate surface. A pause between pulses of the firstsource gas and the second source gas may be about 2.0 second or less,about 1.0 seconds or less, or about 0.5 seconds or less. A pause afterthe pulse of the first source gas may also be about 2.0 second or less,about 1.0 seconds or less, or about 0.5 seconds or less. In some

embodiments, at least a portion of a pulse of the first source gas maystill be in the chamber when at a least a portion of a pulse of thesecond source gas enters, so that a primer chemisorption enhanced byco-reaction takes place on the surfaces of the substrate.

In some embodiments, forming the dielectric layer at 104 may includeexposing the substrate to a first source gas, as shown at 106. In someembodiments, such as where a metal silicate dielectric layer is formedvia an ALD process, the first source gas may comprise a siliconprecursor and an oxidizer. The oxidizer may act as a catalyst withrespect to the silicon precursor to increase its reactivity whileeliminating gas-phase reactions. The first source gas forms a firstlayer of silicon and oxygen on the surface of the substrate.

The silicon precursor may comprise any suitable silicon containingprecursor such as, silicontetrachloride (SiCl₄), silane (SiH₄), disilane(Si₂H₆), chlorosilane, dichlorosilane (SiH₂Cl₂), or hexachlorodisilane(Si₂Cl₆), or the like. In some embodiments, the silicon precursor may bea vaporized liquid precursor, such as tris[dimethylamino]silane([((CH₃)₂)N]₃SiH). (TDMAS). The TDMAS may be provided between about 5 toabout 50 mg/min, for example, about 20 mg/min.

The oxidizer may comprise water vapor (H₂O), oxygen (O₂), ozone (O₃),nitrogen oxides (e.g., N₂O, NO, N₂O₅, NO₂), or the like. In someembodiments, the oxidizing gas is produced from a water vapor generating(WVG) system that is in fluid communication to the process chamber 200.The WVG system generates ultra-high purity water vapor by means of acatalytic reaction of O₂ and H₂. The WVG system has a catalyst-linedreactor or a catalyst cartridge in which water vapor is generated bymeans of a chemical reaction, unlike pyrogenic generators that producewater vapor as a result of ignition. Regulating the flow of H₂ and O₂allows the concentration to be precisely controlled at any point from 1%to 100% concentrations. In some embodiments, the ratio of O₂ to H₂ isbetween about 14:20 to about 21:20, or about 21:20. The water vapor maycontain water, H₂, O₂ and combinations thereof. Suitable WVG systems arecommercially available, such as the WVG by Fujikin of America, Inc.,located in Santa Clara, Calif. and the CSGS (Catalyst Steam GeneratorSystem) by Ultra Clean Technology, located in Menlo Park, Calif.

In some embodiments, the first source gas comprising the siliconprecursor may be provided in one or more pulses at a flow rate betweenabout 5 to about 50 mg/min for a time period of up to about 2 seconds.In some embodiments, the first source gas is not pulsed and provided ata constant flow rate of between about 5 to about 50 mg/min for a timeperiod of between about 1 to about 5 seconds. In some embodiments, theoxidizer may be provided at least in a portion of one or more pulses ofthe first source gas at a flow ratio of between about 14:20 to about21:20 for a time period of between about 0.5 to about 2 seconds.

Next, at 108, the substrate may be exposed to a second source gas. Insome embodiments, the second source gas may comprise a metal precursorand a silicon precursor. The second source gas forms a second layercomprising the metal and silicon atop the first layer. The first layerand second layer react, forming the dielectric layer.

In some embodiments, for example, such as where a hafnium silicatedielectric layer is formed, the metal precursor may comprise (RR′N)₄Hfwhere R or R′ may independently be one of hydrogen, methyl, ethyl,propyl or butyl. In some embodiments, the hafnium precursor may be avaporized liquid precursor, such as tetrakis[diethylamino]hafnium[Hf[N(C₂H₅)₂]₄] (TDEAH). The TDEAH may be provided between about 5 toabout 50 mg/min, or at about 8 mg/min.

The silicon precursor may comprise any suitable silicon containingprecursor such as, silicontetrachloride (SiCl₄), silane (SiH₄), disilane(Si₂H₆), dichlorosilane (SiH₂Cl₂) or the like. In some embodiments, thesilicon precursor may be a vaporized liquid precursor, such astris[dimethylamino]silane [(CH₃)₂)N]₃SiH] (TDMAS). The TDMAS may beprovided between about 5 to about 50 mg/min, or about 20 mg/min. In someembodiments, the silicon precursor may be the same silicon precursor asused in the first source gas at 106.

In some embodiments, the second source gas may be provided in one ormore pulses at a flow rate between about 5 to about 50 mg/min for a timeperiod of up to about 5 seconds. The metal precursor and siliconprecursor may be provided at a flow rate ratio of metal precursor tosilicon precursor between about 8:50 to about 8:20.

In some embodiments, the second source gas may be provided prior to thefirst source gas. For example, in some embodiments, such as where ametal silicate dielectric layer is formed via an ALD process, the firstsource gas may comprise a metal precursor and a silicon precursor andthe second source gas may comprise a silicon precursor and an oxidizer.In such embodiments, the substrate may first be exposed to a source gascomprising a metal precursor and a silicon precursor to form a firstlayer of the metal and silicon. The substrate may then be exposed to anoxidizer and a silicon precursor forming a second layer of silicon andoxygen, which reacts with the first layer, forming the metal silicatedielectric layer.

In any of the above embodiments, the flow rates and/or durations of eachpulse may be the same or may vary over the course of the total pulsesrequired to form a particular dielectric layer, thereby facilitatinglayers having either uniform or graded compositions.

In any of the above embodiments, each cycle consisting of a pulse of thefirst source gas, and pulse of the second source gas, provides a hafniumsilicate layer having a thickness between about 1.0 and about 1.2 Å. Thealternating sequence may be repeated until the desired thickness isachieved. Accordingly, the deposition process may require between 10 and50 cycles, or between about 50 and 150 cycles.

In addition to the foregoing, additional process parameters may beregulated while depositing the dielectric layer to the desiredthickness. In some embodiments, the process chamber may be maintained ata pressure of between about 0.5 to about 1 Torr. In some embodiments,the temperature of the process chamber is maintained at a temperaturebelow the precursor thermal decomposition limit to suppress a gas-phasereaction. In some embodiments, the temperature of the process chambermay be maintained below 300 degrees Celsius. In some embodiments, thesubstrate temperature may be maintained between about 150 degreesCelsius to about 200 degrees Celsius. The processing time may be set ata predetermined processing period or after a desired thickness of thedielectric layer is deposited on the substrate. In some embodiments, theprocessing time may be between about 360 to about 3600 seconds.

In any of the above embodiments, an inert gas, such as argon, helium,hydrogen, nitrogen, or the like, may also be provided to the processchamber. For example, in some embodiments, each pulse may be performedsequentially, and may be accompanied by a flow of an inert gas at a ratebetween about 450 sccm and about 1500 sccm, or about 900 sccm. The inertgas may also be provided to the process chamber subsequent to eachexposure of the substrate to the first of second source gas. The inertgas may be pulsed between each pulse of the reactive compounds. Forexample in some embodiments, the inert gas may be provided between about1000 to about 2500 sccm, or about 2200 sccm, for up to about 12 secondsto the process chamber between exposing the substrate to the firstsource gas and the second source gas or between the second source gasand the first source gas. In some embodiments, the inert gas may becontinuously provided to the process chamber throughout the process atthe same rates as discussed above, or in some embodiments, less.

The flow of inert gas, whether pulsed or continuous, may facilitateremoving any excess reactants from the reaction zone to prevent unwantedgas phase reactions of the reactive compounds, and may also remove anyreaction by-products from the processing chamber, similar to a purgegas. In addition to these benefits, the continuous flow of non-reactivegas helps deliver the pulses of reactive compounds to the substratesurface similar to a carrier gas.

Next, at 110, it is determined whether the dielectric layer has achieveda predetermined thickness. If the predetermined thickness has beenachieved the method 100 ends at 112 and the substrate can proceed forany further processing. If the predetermined thickness has not beenachieved, the method 100 returns to 104 to continue forming thedielectric layer.

Although the embodiments of the invention are described to deposithafnium-containing compounds, a variety of metal oxides and/or metalsilicates may be formed outside of the hafnium-containing compounds byalternately pulsing metal precursors with oxidizing gas derived from aWVG system, such as a fluid of water vapor. The ALD processes disclosedabove may be altered by substituting the hafnium and/or siliconprecursors with other metal precursors to form materials, such ashafnium aluminates, titanium silicates, zirconium oxides, zirconiumsilicates, zirconium aluminates, tantalum oxides, tantalum silicates,titanium oxides, titanium silicates, silicon oxides, aluminum oxides,aluminum silicates, lanthanum oxides, lanthanum silicates, lanthanumaluminates, nitrides thereof, and combinations thereof.

FIG. 2 is a schematic cross-sectional view of an embodiment of anapparatus 200 that may be used to perform embodiments of the presentinvention. The apparatus may be any suitable apparatus for processingsubstrates, for example, the GEMINI ALD chamber, available from AppliedMaterials, Inc., of Santa Clara, Calif.

The process chamber 200 generally comprises a chamber body 210 having aninner volume 234 with a substrate support 212 disposed therein. Thechamber body 210 further comprises sidewalls 204 and a bottom portion206. A slit valve 208 disposed in a sidewall 204 of the chamber body 210provides access for a robot (not shown) to deliver and retrieve asubstrate 220.

A substrate support 212 supports the substrate 220 on a substratereceiving surface 214. The substrate support (or pedestal) 212 ismounted to a lift motor 228 to raise or lower the substrate support 212and a substrate 220 disposed thereon. A lift plate 216 coupled to a liftmotor 218 is mounted in the process chamber 200 and raises or lowerspins 222 movably disposed through the substrate support 212. The pins222 raise or lower the substrate 220 over the surface of the substratesupport 212. In some embodiments, the substrate support 212 includes avacuum chuck, an electrostatic chuck, or a clamp ring for securing thesubstrate 220 to the substrate support 212.

The substrate support 212 is heated to increase the temperature of thesubstrate 220 disposed thereon. For example, the substrate support 212may be heated using an embedded heating element, such as a resistiveheater or may be heated using radiant heat, such as heating lampsdisposed above the substrate support 212. A purge ring 224 is disposedon the substrate support 212 to define a purge channel 226 whichprovides a purge gas to a peripheral portion of the substrate 220 toprevent deposition thereon.

An exhaust system 230 is in communication with a pumping channel 232 toevacuate any undesirable gases from the process chamber 200. The exhaustsystem 230 also helps in maintaining a desired pressure or a desiredpressure range inside the process chamber 200.

The gas delivery system 250 is coupled to the chamber body 210 toprovide precursor(s), carrier gases and/or purge gases to the processchamber 200. The gas delivery system 250 includes a gas source 252 and aconduit 256. The conduit 256 couples the gas source 252 to the processchamber 200. In some embodiments, the gas delivery system 250 maycomprise additional elements to facilitate providing a plurality ofdifferent gases in a continuous flow or by pulsing. For example,multiple gas sources may be included to provide multiple gases.Additionally, one or more valves, such as a switching valve, high speedvalve, stop valve, or the like, may be included to facilitate pulsingeach source gas.

In some embodiments, for example, such as where a solid or liquidprecursor is utilized, the gas delivery system 250 may also comprise oneor more ampoules. In such embodiments, the one or more ampoules may beconfigured to allow the solid or liquid precursor to be contained andsublime into gaseous form for delivery into the process chamber 200.

Returning to FIG. 2, at least a portion of a bottom surface 272 of achamber lid 270 may be tapered from an expanding channel 274 to aperipheral portion of the chamber lid 270. The expanding channel 274improves velocity profile of gas flow from the expanding channel 274across the surface of the substrate 220 (i.e., from the center of thesubstrate to the edge of the substrate). In some embodiments, the bottomsurface 272 comprises one or more tapered surfaces, such as a straightsurface, a concave surface, a convex surface, or combinations thereof.In some embodiments, the bottom surface 272 is tapered in the shape of afunnel. The expanding channel 274 is one exemplary embodiment of a gasinlet for delivering the sublimed precursor and carrier gas from theconduit 256 to the substrate 220. Other gas inlets are possible, forexample, a funnel, a non-tapering channel, nozzles, showerheads, or thelike.

A controller 240, such as a programmed personal computer, work stationcomputer, or the like is coupled to the process chamber 200.Illustratively, the controller 240 comprises a central processing unit(CPU) 242, support circuitry 244, and a memory 246 containing associatedcontrol software 248. The controller 240 controls the operatingconditions of processes performed in the process chamber, such as, forexample, an ALD process. For example, the controller 240 may beconfigured to control the flow of various precursor gases and purgegases from the gas delivery system 250 to the process chamber 200 duringdifferent stages of the deposition cycle.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A method for forming a dielectric layer on a substrate, comprising:(a) exposing the substrate to a first source gas comprising a silicon(Si) precursor and an oxidizer for a first period of time to form afirst layer comprising silicon and oxygen; and (b) exposing thesubstrate to a second source gas comprising a metal precursor and thesilicon precursor for a second period of time to form a second layercomprising silicon and a metal, where in the first layer and the secondlayer form the dielectric layer.
 2. The method of claim 1, wherein thedielectric layer comprises hafnium silicate (HfSiO), hafnium siliconnitride (HfSiN), or aluminum silicon oxynitride (AISiON).
 3. The methodof claim 1, wherein the silicon precursor comprises at least one ofsilicontetrachloride (SiCl₄), silane (SiH₄), disilane (Si₂H₆),chlorosilane (SiH₃Cl), dichlorosilane (SiH₂Cl₂), trichlorosilane(SiHCl₃), hexachlorodisilane (Si₂Cl₆), or tris[dimethylamino]silane([((CH₃)₂)N]₃SiH).
 4. The method of claim 1, wherein the oxidizercomprises at least one of water vapor (H₂O) or ozone (O₃).
 5. The methodof claim 1, wherein a flow rate ratio of the silicon precursor to theoxidizer is about 14:20 to about 21:20.
 6. The method of claim 1,wherein the first source gas and the second source gas are each providedat a flow rate of about 5 to about 50 mg/min.
 7. The method of claim 1,wherein the first period of time is up to about 2 seconds.
 8. The methodof claim 1, wherein the metal precursor comprises at least one ofhafnium tetrachloride (HfCl₄), hafnium fluoride (HfF₄), hafnium bromide(HfBr₄), or tetrakis[diethylamino]hafnium (Hf[N(C₂H₅)₂]₄).
 9. The methodof claim 1, wherein a flow rate ratio of the metal precursor to thesilicon precursor is about 8:50 to about 8:20.
 10. The method of claim1, wherein the second period of time is up to about 3 seconds.
 11. Themethod of claim 1, further comprising: repeating (a) and (b) to form thedielectric layer to a desired thickness.
 12. The method of claim 1,further comprising: supplying an inert gas for a period of time whileperforming at least one of (a) or (b).
 13. The method of claim 1,further comprising: purging the process chamber with an inert gasbetween performing (a) and (b).
 14. The method of claim 1, wherein thefirst source gas or second source gas further comprises an inert gas.15. The method of claim 1, further comprising: maintaining the processchamber at a temperature of about 150 to about 300 degrees Celsius. 16.A computer readable medium, having instructions stored thereon which,when executed by a controller, causes a process chamber having asubstrate disposed therein to have a dielectric layer formed thereon bya method, the method comprising: (a) exposing the substrate to a firstsource gas comprising a silicon (Si) precursor and an oxidizer for afirst period of time to form a first layer comprising silicon andoxygen; and (b) exposing the substrate to a second source gas comprisinga metal precursor and the silicon precursor for a second period of timeto form a second layer comprising silicon and a metal, wherein the firstlayer and the second layer form the dielectric layer.
 17. The computerreadable medium of claim 16, wherein the method further comprises:repeating (a) and (b) to form the dielectric layer to a desiredthickness.
 18. The computer readable medium of claim 16, wherein themethod further comprises: maintaining the process chamber at atemperature of about 150 to about 300 degrees Celsius.
 19. The computerreadable medium of claim 16, wherein the method further comprises:purging the process chamber with an inert gas between (a) and (b). 20.The computer readable medium of claim 16, wherein the method furthercomprises: supplying an inert gas for a period of time while performingat least one of (a) or (b).